Veteran Owned

Veteran Owned and Operated

Observation/Monitoring Well Installation

Usually with Pase II studies for site closures it is necessary to assess the ground water via monitoring wells. If ground water occurs on the subject site selected soil borings can be converted into observation/monitoring wells that can be for temporary or long-term use. There can be several purposes for these wells including: ground water sampling, photoionization detector measurements, determination of the water table elevation, determination of hydro-geological characteristics and possibly for injection of fluids that will decompose contaminates.

Unless otherwise specified general observation/monitoring wells include Schedule 40 PVC riser pipes, one or two inches in diameter, Schedule 40 flush joint screens, one to ten feet in length that are slotted 0.010 inch that are threaded to a riser pipe of the appropriate diameter length. The screen slot size is dependent on the physical characteristics of the water - bearing zones and indigenous soils. It should be noted that the Michigan Department of Environmental Quality requires, with exceptions, that the screens be of five foot length.

A filter pack, typically a 10/20 mesh sand, will be installed around the screen of the well. The type of filter pack is dependent on the characteristics of the water-bearing zone. The filter pack is placed no more than two feet below and above the well screen as an augur is raised. The top of the pack will be sounded with a weighted tape to monitor for sand bridging. Bentonite will be grouted upwards from the sand pack. The installation could include the use of bentonite chips or the pouring of a bentonite slurry through a tremmie pipe into the annular space between the well and the inner diameter of the hallow stem augur for deep wells. Usually if the top of the filter pack is less than seven feet below grade, bentonite chips can be poured down the space between the well and the riser and then packed.

The PVC riser pipe will extend to approximately 0.5 feet below grade. For permanent wells, an eight-inch flush mounted manhole cover anchored in cement will protect the well. A locking expandable cap will be installed on each riser with a bolt-down manhole cover.

To maximize well yield and provide sediment-free ground water, the well must be developed. A surge block is used in the well for several minutes to force water in and out of the water-bearing zone which will release flow-inhibting fine particles from the borehole and well screen. Then a pump is used to remove several volumes of water out of the well until the ground water is free of sediment. Recharge rates are periodically monitored to determine the condition of the well. For contaminated sites, water from each well must be held in DOT approved 55-gallon drums pending proper disposal unless there is regulatory approval to return the water to the well.

The monitoring wells must be properly closed after the work is completely finalized according to MDEQ regulations.

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